A more thorough explanation:

Definition: A knight of the post is a person who is hired to give false testimony in court.

Example: John was a knight of the post who was paid to lie in court and provide false evidence to help his client win the case.

Explanation: A knight of the post is a person who is willing to lie under oath for money. They are often hired by people who want to win a court case but do not have enough evidence to do so. The example illustrates how John was hired to provide false evidence in court to help his client win the case. This is an illegal and unethical practice that undermines the justice system.